UV Mapping Plane Single Side
This is the default or norm in Blender to have the texture appear on both sides. There is no setting to change this. This also doesn't need to be changed often as usually only one side of a model is showing.

The way I go around this to have the material appear only on one side is to use material nodes and have the base material on one side and a transparent material on the other.

It is a bit tricky if you don't have any experience with material nodes but just follow the node layout and it should work.

Just unwrap and texture as normal and setup your material and then add a second one, enable Transparency, set the Alpha to 0 and turn off the specularity.

As you can see below, both planes have textures but only one shows up when rendered. That is because I have added a transparent material to it along with the normal material and used the Geometry node to pass the materials to the different sides. One of the planes is on one side and the other is rotated 180 degrees around to the other side.



Here is the node setup for the material. (larger image here)